Cognitive operations like selective attention are thought to involve coordinated activity of neuronal ensembles in multiple brain areas. It is abundantly clear that attention enhances visual responses within local ensembles of neurons throughout the visual system, the corollary idea that attention also facilitates the transmission of visual inputs between neuron ensembles in different cortical layers and in different cortical regions has not been thoroughly investigated. Similarly, while it is generally agreed that attentional modulation of low level visual processing is controlled by a higher order network, the specific circuits and physiological processes by which top-down control is imposed are not well understood. With these two problems in mind the overall goal of this project is to define the magnitude and physiological mechanisms of attention's influence on feedforward communication in low level visual processing. Using a combination of spike correlation, standard coherence and Granger causality analyses, we will analyze data from multielectrode recordings in V1 and V2 in monkeys performing a single, well-studied (intermodal) attention task. We have shown that because of the predictability of stimulus rhythms in this paradigm, attention can use low frequency oscillations as instruments to enhance neuronal responses to task relevant stimuli. This finding has wide ramifications because rhythm and predictability are prominent in many aspects of natural behavior. To follow it up, we will test the hypothesis that attention can use low frequency oscillatory phase synchrony to facilitate feedforward communication between neuronal ensembles in the visual pathways. Our specific aims are: 1) to characterize attention's influence on feedforward transmission between cortical layers, 2) to characterize attention's influence on transmission between V1 and V2, and 3) to define the brain mechanisms underlying attentional modulation of interlaminar and interareal interactions. Concurrent sampling of laminar current source density (CSD) and multiunit activity (MUA) profiles in V1 and V2 will index synaptic activity and firing patterns in neuronal ensembles at key locations in the supragranular, granular and infragranular layers. Laminar profiles of attention effects in V1 and V2, along with Granger causality analyses will help to differentiate between several of the alternative control circuits. Single trial analysis of both pre- stimulus and poststimulus oscillatory dynamics and of related variations in neuronal firing patterns in these locations will help to relate dynamics to underlying physiology. PUBLIC HEALTH RELEVANCE: Our methods allow use of the monkey as a model for understanding the neuronal mechanisms of ERP and EEG generation in humans. This study will also provide a data set that can be used to evaluate new functional connectivity analyses developed for use in humans, particularly those targeting the study of epilepsy.